Cellulose esters are valuable polymers, which are useful in many plastic, film, coating and fiber applications. In coatings applications, cellulose esters are generally applied from organic solvent solutions.
U.S. Pat. No. 4,520,192 describes a process for preparing carboxyalkyl acetyl celluloses with a carboxyalkyl degree of substitution per anhydroglucose unit (DS) of 0.2-2.5 and an acetyl DS of 0.5-2.8 and the metal salts of these materials. The preparation of the carboxyalkyl acetyl cellulose is accomplished by converting carboxyalkyl cellulose, sodium salt, into its acid form by soaking in an aqueous acid solution of sulfuric acid, hydrochloric acid, nitric acid, or acetic acid. This is followed by washing with water, solvent exchange of the water with acetic acid, and reaction with acetic anhydride in the presence of a catalyst (sulfuric acid, perchloric acid, sulfoacetic acid or zinc chloride) to give a trisubstituted carboxy acetyl cellulose, i.e., carboxymethyl cellulose acetate, upon precipitation into water. They also claim a process for converting the carboxyalkyl acetyl cellulose product (acid form) to its corresponding sodium, potassium, calcium, or ammonium carboxylate salt. The acid forms of the trisubstituted carboxyalkyl acetyl celluloses were insoluble in water and aqueous lower chain alcohol solutions. These materials were soluble in acetone and methylene chloride/ethanol 9/1. The sodium salt of the carboxyalkyl acetyl cellulose was soluble in water, an aqueous lower alkyl alcohol containing a large amount of water, or aqueous acetone; however, it was insoluble in methylene chloride/ethanol 9/1. We believe this process to yield a product containing an unneutralized strong acid with high sulfur levels. Consequently, this ester would be unstable under general drying conditions or other heat treatment. The process for converting the sodium salt form of carboxymethyl cellulose to the acid form is also described in Swiss Patent No. 247,440 by soaking in 10% sulfuric acid solution.
U.S. Pat. No. 3,435,027 describes a base catalyzed (sodium hydroxide) esterification of carboxymethyl cellulose (in the sodium salt form) in 70-85% acetone nonsolvent media with acetic, propionic, lactic, or stearyl anhydride. The procedure yields a product with a low degree of ester substitution and falls well short of a fully substituted cellulose. This reference claims a base catalyzed process for preparing cellulose ether-esters (containing from 0.1-18% acetyl, which corresponds to 0.01-0.97 DS (acetyl) from a water soluble cellulose ether in a nonsolvent media and products thereof.
USSR Patent 612933 describes a process for preparation of cellulose acetate ethers wherein an alkali activated cellulose (12% sodium hydroxide) is etherified with monochloroacetic acid followed by esterification with acetic anhydride in the presence of sulfuric acid catalyst. The process is limited to a low DS of the carboxymethyl substituent.
U.S. Pat. No. 3,789,117 discloses a process for preparing an enteric medicament coating from an organic solvent soluble cellulose derivative. The cellulose derivative's substitution has a carboxymethyl DS range of 0.3 to 1.2 in conjunction with at least one of the remaining hydroxyl groups being etherified or esterified. Ester groups, of which they do not indicate the degree of substitution, include acetyl, propionyl, butyryl, nitric, or higher fatty acids.
RO 96929 describes a carboxymethyl cellulose (CMC) acetate with a carboxymethyl degree of substitution of 0.5-3.0, acetyl DS of 0.4-2.9, and viscosity 150-1500 cP. This material was taught to be useful as an alkaline suspension stabilizer, solution thickener, and alkaline media binder. The material was prepared by mixing 70% acetic acid with CMC(Na salt), washing the acetic wet CMC with 50% acetic acid to remove the sodium acetate, and esterification of the acetic acid wet CMC--H with acetic anhydride for 1.5 hours at 50-110.degree. C. in the presence of sulfuric acid.
U.S. Pat. No. 5,008,385 reports cellulose derivatives that can be synthesized by homogeneous reaction in dimethylacetamide and/or N-methylpyrrolidine containing LiCl. Included in their examples was CMC acetate (carboxymethyl DS 0.13-0.23, acetyl DS 2.54-2.15). These materials were tested for use in the production of fibers, filaments, or membranes.
Carbohydrate Research, 13, pp.83-88, (1970) describes the preparation of CMC acetate by sulfuric acid catalyzed acetylation of CMC (carboxymethyl DS of 0.07) hydrolysis (acetylation and hydrolysis procedures taken from Maim, Ind. Eng. Chem., 38 (1946) 77), and evaluation of this material in membranes for reverse osmosis.
Holzforschung, 27(2), pp. 68-70, (1973) describes the rate of carboxymethylation and deacetylation of cellulose acetate in the presence of sodium hydroxide. This work showed that deacetylation and carboxymethylation occur simultaneously with the rate of deacetylation being faster than the rate of carboxymethylation. The highest carboxymethyl DS obtained was less than 0.1.
GB 2,284,421 discloses carboxymethyl cellulose alkanoates which are "lightly carboxymethylated", i.e., having a degree of substitution per anhydroglucose unit of less than 0.2. Such polymers are taught to be useful as a coating agent for paper and papermaking or as a bonding agent for non-woven fabric, or can be extruded to form filaments or film, or can be used to produce shaped articles or a sponge.
Numerous patents mention the use of polymer coatings on the surface of pigments to either protect the surface of the pigments from reaction or to prevent agglomeration of the pigment particles. Elaborate means are taken to prevent the agglomeration of pigment particles in both solvent and waterborne dispersions. For example, U.S. Pat. No. 5,558,705 teaches binding organic pigments with metallic pigments and polymeric materials to prevent agglomeration. However, no mention is made of aqueous pigment dispersions.
Similarly, U.S. Pat. No. 4,725,317 suggests the use of pigments, polymeric binders, and organic solvents to form a solvent free, free-flowing metallic pigment or pigment composition which is non-dusting. This is achieved by coating the pigment particles followed by evaporating the solvents. Polymeric binders such as cellulose esters, cellulose ethers, acrylic ester resins, polyester resins, alkyd resins, etc. are mentioned. However, the patent teaches that metallic particles or pigments must be dried with the coating on the surface in order to add the pigments to water. By adding additional steps in processing, the cost of manufacturing increases. Furthermore, it may be desirous to use pigments or particles that have not been manufactured in such a process, due to the limited availability of pigments processed in the above manner.
Research Disclosure 40055 discusses polished spherical aluminum pigments that can be easily dispersed in solvents without agglomerating, due to their spherical shape. They can be added to a polymer system with minimal shear. However, because the aluminum particles are spheres rather than flat disks or similar shape, they cannot contribute to metallic flake orientation or metallic flop. Therefore, the spheres must be added with other aluminum flakes to achieve brightness or improved flop. U.S. Pat. No. 5,593,773 mentions new shapes of particles to provide better metallic flop and orientation. Metallic flop and orientation are also described in U.S. Pat. No. 4,590,235. The patent does not mention the use of binders, particularly those that enable metallic flake to beincorporated into aqueous systems.
It is known in the art that it is necessary to passivate or coat aluminum pigment particles to prevent reaction with water to form hydrogen gas when such particles are used in an aqueous system. Although GB 2,185,936 discloses a method for coating aluminum by a blown film procedure to manufacture a metal polymer film laminate, it does not mention any improvement in wetting of the aluminum in aqueous systems. EP 0 673 980 A states that lamination of aluminum film can be used to form "glitter" or "flitter" flakes by cutting the aluminum film. Delamination in such a procedure can be a problem in the preparation of metallic flake pigments. European Patent Application 134,676 teaches that heating metallic flake particles in the presence of an oxygenated atmosphere followed by coating with polyethylene wax protects the surface. No mention is made in either reference, of adding a polymeric binder resin to improve the wetting of the metallic flake. U.S. Pat. No. 5,637,143, suggests the protection of the surface of metal particles with heteropolyanion compounds, and phosphosilcate compounds to increase their stability against attack by water.
Prevention of agglomeration of metallic particles in the art is usually achieved by dilution of the metallic particles with solvents. However, in aqueous coatings, there stands a desire to reduce the amount of volatile organic solvents, without having to go to elaborate methods of specially coating aluminum flake or pigments in order for them to disperse easily in aqueous systems.